ALTITUDINAL VARIATIONS IN GERMINATION AND GROWTH-RESPONSES OF REYNOUTRIA-JAPONICA POPULATIONS ON MT FUJI TO A CONTROLLED THERMAL ENVIRONMENT

The authors examined altitudinal variations in the thermal responses o f seed germination and seedling growth in Reynoutria japonica (= Polyg onum cuspidatum) under controlled environmental conditions. Seed popul ations were collected from different altitudes on Mt Fuji in Japan. Th e mean seed weight of the upland populations (above 1500 m) was signif icantly (1.5-fold) heavier than that of the lowland populations (below 1400 m). Under the lowest temperature regime of 15/10-degrees-C (day/ night) the upland populations showed a significantly higher percentage and speed of germination than the lowland populations; this was not s ignificant under higher temperature regimes. These results indicate th at the germination traits of the upland populations on Mt Fuji are fav orable for colonization in their cold habitats (low temperature and sh ort growing season). Growth and shoot development were compared betwee n the seedlings grown from seeds collected at altitudes of 700 and 242 0 m. The upland seedlings showed a significantly larger biomass and le af area than the lowland seedlings at 15-degrees-C, but there was no d ifference at 25-degrees-C. The difference in biomass at 15-degrees-C w as attributed to the difference in seed weight. The upland seedlings p roduced a significantly larger number of branches with smaller and mor e numerous leaves at both 15-degrees-C and 25-degrees-C. These develop mental traits of the upland seedlings were considered to represent the adaptation of the life form to upland environments. It was concluded that the R. japonica populations along an altitudinal gradient on Mt F uji can be classified into two ecotypes, whose distribution border lie s at an altitude of about 1400-1500 m. In this study, the seed weight and germination traits of two R. japonica seed populations collected i n Chiba Prefecture were briefly compared with those of the lowland pop ulations on Mt Fuji.